UP to 2500 US Marines will be stationed in Australia for six months of every year under a new bilateral defence deal sealed today by Julia Gillard and Barack Obama today.

The agreement will also allow more US ships and military aircraft – including B52 bombers – to operate from Australian bases.

President Obama said the agreement, coming at the 60th anniversary of the ANZUS alliance, reflected the United States’ determination to safeguard security in the Asia-Pacific.

”Because of these initiatives that are the result of our countries working very closely together as partners, we are going to be in a position to more effectively strengthen the security of both our nations and this region,” Mr Obama said after private talks with Ms Gillard today.

”This deepening of our alliance sends a clear message of our commitment to this region – a commitment that is enduring and un-wavering.”

The agreement is set against the background of growing Chinese military spending and the dramatic expansion of the Chinese navy.

Mr Obama said President Obama said the US welcomed the rise of China but “it’s important for them to play by the rules of the road”.

“We will send a clear message to them that we think they may need to be on track, in terms of accepting the rules and responsibilities of being a world power.”

Putting 2,500 U.S. Marines in the Darwin area is significant. It’s farther afield from China than is Guam, but still close enough to be “in the neighborhood.” Think of this as a “diversification” of the American defense portfolio in the region. While 2,500 Marines might not sound like a whole heck of a lot, numbers-wise, it is roughly equivalent to the number of Marines found in a Marine Expeditionary Unit (MEU), which are employed to such great effect off of U.S. Navy amphibious shipping assets around the globe. I would imagine that if these Marines based in Australia were to be employed operationally in the region, it would be in a MEU-like capacity, meaning that the modular expansion to a Marine Expeditionary Brigade (MEB) or Marine Expeditionary Force (MEF) would also be possible based on the size of the contingency.